Latest Prognosis for Mystery Bertha "Obstruction": Early January
Seattle waterfront tunnel planners say it will be next year before they know what's blocking Bertha, the world's largest tunnel-boring machine.
Matt Preedy, deputy WSDOT viaduct replacement program administrator, and Chris Dixon, project manager with Seattle Tunnel Partners, said today that the effort to identify what's blocking Bertha, the downtown tunnel-drilling machine that has been stopped by an obstruction or mechanical problem for the past two weeks, will stretch into the new year.
At a press conference at the Milestone 31 viaduct museum today (and not, mercifully, at Pier 48, where Bertha is stuck and where press updates have routinely been held), Preedy said tunnel engineers were removing water from the tunnel-boring site via six (and soon more) drills in an effort to reduce the pressure around Bertha so that workers can descend to the level of the machine, which is currently about 50 feet below ground.
The depressurizing process also involves inreasing pressure within the chamber of the tunnel boring machine; too much pressure, Dixon said, and the contractors risk "a blowout or a leakage to the surface" in which "there's no way of holding air or water back."
Conversely, without the depressuring effort, Preedy said, "it would feel like you're in the bottom of a 50-to-100-foot-deep swimming pool."
The idea is that workers will first go inside the machine itself, via two "manlocks," to see if they can identify the cause of the obstruction. If that doesn't work, the tunnel contractors will have to send in divers, who will have to go through compression and decompression to deal with the pressure created by 50 feet of water.
"Realistically," Preedy said, "we’re not going to be able to get people into the machine … and really see what’s going on, probably, until the beginning of next year." At that point, Dixon said, the tunneling team will remove the blockage, possibly after breaking it up into pieces.
Neither Preedy nor Dixon was willing to hazard a guess as to how much the current tunnel hassle will delay tunnel construction or add to the cost of the project.
"Until we determine what the situation is, we can’t say who’ll be liable for additional costs or delays," Dixon said. "We don’t know what he extent of the delay is going to be or what the additional cost of the delay will be."